Catalyzed reactions and associated catalytic reactor systems are widely used in a variety of industries. A catalyst typically has a finite performance life, which may include one or more cycles of catalyst activity separated by regeneration cycles. For example, as a catalytic process continues over time, the catalyst activity generally decreases. When the catalyst activity reaches a point at which it no longer efficiently catalyzes the process, the catalyst may be at the end of its life or at the end of one of its cycles of catalyst activity. If the catalyst has one or more cycles of catalyst activity remaining, the catalyst can be regenerated to begin a new cycle of catalyst activity. If no additional cycles are available, the catalyst life is spent, and the spent catalyst typically will need to be replaced with fresh catalyst.
FIG. 1 is a hypothetical graph illustrating a general catalyst life cycle for a catalyst having 4 activity cycles and 4 regeneration cycles. The first activity cycle begins a time zero and lasts for many months, and during this cycle the activity of the catalyst decreases as evidenced by an increase in the reactor inlet temperature (as described in more detail herein). The slope of the line represents the fouling rate of the catalyst, i.e., the change in activity over a given period of service time. The reactor inlet temperature continues to increase until it reaches a maximum value (e.g., greater than 1000° F. in FIG. 2), at which time the catalyst may be regenerated (e.g., a regeneration cycle), for example by subjecting the catalyst to a high temperature oxidation (e.g. greater than about 600° F.) to remove carbon build-up such as coking. During this process coke may be removed from the catalytic reactor system, and the catalyst contained therein. The regeneration of the catalytic reactor system provides renewed activity to the catalyst (e.g., a new activity cycle) as evidenced by a lower reactor inlet temperature, which is shown by the vertical drops or decreasing steps in the graph. However, when a new cycle is started, the starting reactor inlet temperature is typically higher than for the previous cycle (as shown by the progressively increasing reactor inlet temperature at the start of each new cycle), representing an unrestored loss in overall catalyst activity. Because the catalyst activity is not fully restored after each cycle, the catalyst life is limited by a maximum number of regeneration cycles, for example four as shown in FIG. 1. Furthermore, with each regeneration cycle, the fouling rate (slope) of the catalyst may increase. Thus, regeneration of a catalytic reactor system may also increase the catalyst fouling rate, which would further reduce the total life of a catalyst.
The catalytic reactor system may require service for a variety of reasons which may occur at various points throughout the catalyst life cycle. In preparation for servicing, any hazardous substances present in the reactor system need to be abated to a safe exposure level such that the reactor system may be opened for service. Typically, a catalytic reactor system regeneration procedure is performed to abate the hazardous substances to a safe exposure level, and subsequently a new catalyst activity cycle is begun after the servicing. When a shut down is necessary at a time prior to the end of a catalyst's life or one of its cycles, useable catalyst activity is lost during the regeneration. Therefore, a need exists for methods of abating hazardous substances to a safe exposure level for servicing a catalytic reactor system that can preserve catalyst activity and thereby improve overall plant economics.